In a conventional digital moving image communication system, in a case where an error packet is received at the reception side, the reception side sends to the transmission side a retransmission request in relation to a part (i.e., block, slice, or the like) which could not correctly be decoded due to such an error. Then, the transmission side which received the retransmission request from the reception side retransmits to the reception side the encoded data corresponding to the retransmission-requested part which could not correctly be decoded.
Moreover, on the reception side, the number of times of retransmission, a loss factor of information, an interval of inserting an intra-frame encoded frame, and the like are set as the parameters, and retransmission request priority for setting a threshold value is determined based on any of the parameters. Then, in regard to the part which could not correctly be decoded, it is determined on the reception side whether or not to send the retransmission request by judging the set threshold value with an arbitrary criterion.
Meanwhile, on the transmission side, there is provided a retransmission priority determination unit which sets the number of times of retransmission, the loss factor of information, the interval of inserting the intra-frame encoded frame, and the like as parameters, and sets a threshold value based on any of the parameters. Then, in a case where the retransmission request sent from the reception side is received, the transmission side determines the process (whether or not to execute retransmission) in response to the retransmission request sent from the reception side by judging the threshold value set by the retransmission priority determination unit with an arbitrary criterion. That is, conventionally, the retransmission control to be executed on the reception side is independent of the retransmission control to be executed on the transmission side.
In the conventional digital moving image communication system, the priority order concerning retransmission request of moving image frames or the blocks constituting the frames are set independently on the transmission side and the reception side, and the transmission side and the reception side operate independently. For this reason, there is a problem that the loads increase on both the transmission side and the reception side.
In particular, if an error is detected on the reception side, it is determined whether or not to execute the retransmission request after calculating and evaluating the priority order, importance and the like of the point where the relevant error occurred. For this reason, there is a problem that it takes a time from the error detection to the judgment as to whether or not to execute the retransmission request.